Draft Tube calculations using OpenFOAM-1.5dev and validation with FLINDT data

Transcription

1 6th OpenFOAM Workshop, June , PennState University, USA Draft Tube calculations using OpenFOAM-1.5dev and validation with FLINDT data C. Devals, Y. Zhang and F.Guibault École Polytechnique de Montréal, Canada T. Vu and B. Nennemann Andritz Hydro, Pointe-Claire, Canada 1

2 Context Viscous flow simulations for hydraulic turbo-machinery design Distributor Spiral casing Runner Draft-tube 2

3 Context Previous work: 25 th IAHR Symposium on Hydraulic Machinery and Systems September 20-24, 2010, Timisoara, Romania Steady and unsteady flow computation in an elbow draft tube with experimental validation T.C. Vu, C. Devals, Y. Zhang, B. Nennemann and F. Guibault International Journal of Fluid Machinery and Systems Vol 4, No 1, January-March 2011 Lt=1%D th Lt=0.5%D th Lt=0.25%D th 3

4 Objectives Understand why the recovery coefficient for Phi=0.368 shows an important decrease for Lt=0.5%D th. Validate OpenFOAM RANS simulations for draft tube on hexahedral meshes Compare recovery coefficient χ prediction with experimental data 4

5 Test Case Description Model draft tube test: FLINDT FLINDT is for FLow INvestigation in Draft Tubes Project (LMH-EPFL Switzerland) Throat diameter: D th = 0.4 m Rotational speed: N=1000 RPM Angular velocity: ϖ= Hz Flow coefficient ϕ: 0.340, 0.360, 0.368, 0.380, and corresponding swirl: 0.332, 0.242, 0.214, 0.198, and Recovery coefficient pstat static pressure difference between inlet and outlet χ = A ref reference section area A ref = m P ρ stat Q A ref 2 ϕ = Q πϖr 3 th 5

6 Physical Properties and Models Steady state Reynolds averaged Navier-Stokes equations Newtonian fluid r r ( U U) r U = 0 ν = ν ρ = ν ν lam lam + ν turb 997kg.m µ = = ρ µ ρ turb turb = = p r r T = ( I + ν ( U + U )) ρ C mu k ρ 2 ε µ = 6 rel m 2 s µ µ turb lam 1 k ε turbulence model 6

7 Boundary Conditions Inlet pressure type zerogradient U, k type profile1dfixedvalue filename "profil-rr.csv" epsilon type turbulentmixinglengthdissipationrateinlet mixinglength U profile k profile 7

8 Boundary Conditions Outlet pressure type fixedmeanvalue meanvalue 0 value uniform 0 U, k and epsilon type zerogradient 8

9 Boundary Conditions pier U type fixedvalue value uniform (0 0 0) p, k and epsilon type zerogradient No slip Wall condition 9

10 Boundary Conditions main U type fixedvalue value uniform (0 0 0) p, k and epsilon type zerogradient No slip Wall condition 10

11 Boundary Conditions ext U type fixedvalue value uniform (0 0 0) p, k and epsilon type zerogradient No slip Wall condition 11

12 Numerical Model Steady state (RANS) calculations (10000 iterations) Solver: SimpleFOAM Convection term discretization: normalized variable diagram (NVD) scheme GammaV (between 0 and 1) Linear solver: PBiCG for all variables except P, GAMG for P Turbulence model: k-epsilon Velocity inlet BC : axi-symmetrically averaged velocity measures Turbulence inlet BC: axi-symmetrically averaged k measures 4 turbulence length scales tested (epsilon) Convergence: tolerance of 1.e-6, reltol of 0.01 for all variables Monitoring variable: pressure recovery factor Pstat χ = 1 Q ρ 2 Aref 2 12

13 Test Cases Mesh investigation # nodes # elements CRS STD FINE Scheme GammaV investigation: ψ=0, ψ=0.5 and ψ=1 GammaV is the improved version of the NVD gamma scheme (ψ=0 best accuracy and ψ=1 more robust) Mixing length investigation: Lt=0.25%D th, 0.5%D th, 1.0%D th and 5%D th Initial conditions investigation 13

14 Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 14

15 Mesh investigation GammaV 1 Coarse mesh Standard mesh Fine mesh 15

16 Mesh investigation GammaV 1 Coarse mesh Standard mesh Fine mesh Phi=0.368 Phi=0.380 X=

17 Mesh investigation GammaV 1 Phi= ct2 ct CFD Experimental Data Steady probe Coarse mesh CFD Experimental Data Steady probe Fine mesh Static Pressure Axial Component Radial Component Tangential Component Energy 17

18 Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 18

19 Scheme investigation GammaV Coarse mesh GAMMAV 0.0 GAMMAV 0.5 GAMMAV

20 Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 20

21 Mixing length investigation Standard mesh GammaV 1 Lt=0.25%Dth Lt=0.50%Dth Lt=1.00%Dth Lt=5.00%Dth 21

22 Mixing length investigation Standard mesh GammaV 1 Relative Viscosity Lt=0.50%Dth Relative Viscosity Lt=5.00%Dth X=0.20 X=0.20 X=0.25 X=0.25 X=0.00 X=0.00 X=-0.25 X=-0.25 X=-0.20 X=

23 Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 23

24 Initial condition investigation Std mesh GammaV 1 Lt=0.25%Dth Initial conditions from no previous calculation Initial conditions from previous calculation 24

25 Conclusions and Perspectives Conclusions Results are quite good compared to experimental data Results are not so sensitive to mesh resolution except for Phi=0.368 Results are sensitive to scheme Results are sensitive to initialization Perspectives Validation and comparison with OpenFOAM-1.6ext Runner and Draft-Tube calculations Unsteady cases Wall function investigation 25

26 Thank you for your listening Any questions? 26